Loop Impedance in Magnetoplasma: Theory and Experiment


  • Graham L. Duff,

  • Raj Mittra


The impedance of a small loop in magnetoplasma is derived for the cases of magnetic field normal to and parallel to the plane of the loop. The quasi-static and uniaxial approximation methods are used, and an argument is given to justify the uniaxial approximation as the more desirable method. The results of the theory are given in analytic form and are evaluated numerically and presented graphically. The loop impedance is seen to be much less plasma-dependent than the impedance of a short electric dipole. It is shown that the small loop can be an efficient radiator under certain plasma conditions. The results of laboratory measurement of loop impedance in magnetoplasma are also given for the cases of normal and parallel orientation of the magnetic field with respect to the plane of the loop. The laboratory plasma is generated by using a brush-electrode configuration. The measured impedance is compared with the theoretical predictions, and good agreement is shown for the perpendicular orientation. Quantitative agreement with the theory is not as good for the case of parallel orientation, but much of the gross impedance behavior is verified for this orientation, particularly the fact that the impedance is relatively plasma-dependent.